NATURAL SCIENCES OF PHILADELPHIA. 267 



Neck farrow moderately well defined ; neck segment very much depressed be- 

 low the other parts, and sloping backwards ; apparently equalling the breadth 

 across between the two outer lobes. 



Surface showing, under a magnifier, small, unequal, ratlier scattering pus- 

 tules, with smaller intermediate granules. 



Lengtb, including the neck segment, 0'70 incb, do. excluding sam<?, 0-52 

 incb; height, (MS inch ; breadth, O9o inch; do. of middle lobe at posterior 

 extremity, 0-25 incb ; do. of same at summit, ()--il inch ; do. of same at front, 

 0-60 inch. 



Compared with the corresponding parts of L. Trentonensis, this species will 

 be at once distinguished, by its much more elevated and differently formed 

 glabella, as well as by its less convex lateral lobes, and the presence of a de- 

 fined furrow between the lateral and the palpebral lobes. Its surface is also much 

 less strongly and distinctly pustulose. This latter character, and its propor- 

 tionally narrower neck segment, as well as its more conical middle lobe, readi- 

 ly distinguish it from L. hibernicus, of Portlock, which it more nearly resem- 

 bles. It differs too distinctly from L. Boltoni, of the Niagara Group, to render 

 a comparison necessary. 



Locality and position. Alexander County, Illinois. Trenton division, 

 Lower Silurian. 



Genus PROETUS, Steininger, 1830. 

 Pkoetus kllipticus, M. & W. 



Ratlier small, entire outline narrow elliptic. Cephalic shield about one- 

 third wider than long, and slightly longer than the thorax, semielliptic, regu- 

 larly and rather narrowly rounded in front and straight behind, with postero- 

 lateral angles produced into small spines, which extend back to the fourth tho- 

 racic segment ; anterior and lateral borders with a narrow marginal rim, 

 strongly deflected upwards, and separated from the cheek and glabella by a 

 deep furrow. Glabella more prominent than the cheeks, including the neck 

 segment, a little more than twice as long as wide, broader behind than in front, 

 where it is regularly rounded, separated from the cheeks ou each side by mode- 

 rately well defined furrows ; neck segment more prominent in the middle than 

 any part of the glabella, about twice as wide (antero- posteriorly) as the tho- 

 racic segments, and defined by a narrower, but distinct neck furrow, the con- 

 tinuation of which becomes wider, but rather less sharply impressed, as it 

 extends straight 'across the posterior margins of the cheeks to their lateral 

 marginal furrows ; lateral furrows of glabella, excepting the posterior ones, 

 nearly obsolete ; posterior lateral lobes small, subovate, and nearly isolated 

 by the rather obscure lateral furrows just in front of each being directed ob- 

 liquely backwards and inwards, so as to intersect the neck furrow ; the other 

 lateral lobes, of which there seems to be indications of two on each side, are 

 very small and nearly obsolete, anterior lobe composing nearly half of the 

 glabella. Eyes lunate, not oblique, one-third as long as the glabella, but not 

 so prominent, situated less than their own length in advance of the posterior 

 margin of the cheeks near the glabella, and about half their length from the 

 lateral margins of the cheeks ; reticulations very fine. Facial sutures inter- 

 secting the posterior margins of the cheeks near the middle, and extending 

 forward from the anterior side of each eye, at first close to the side of the gla- 

 bella, but soon curving outwards and obliquely forward, so as to intersect the 

 lateral margins nearly opposite the anterior end of the glabella. 



Thorax about one-third wider than long, distinctly trilobate ; mesial lobe 

 prominent, about once and a half as wide as the lateral lobe, consisting, ap- 

 parently, of only eight segments ; a little widest near the middle, and taper- 

 ing posteriorly ; segments not arching forward, but strongly arched upward, 

 rather flattened. Lateral lobes depressed, somewhat flattened near the mesial 

 lobe, and rounding down rather distinctly to the lateral margins ; segments 



185,J 



